The fracture of polymeric sheets is one of the practical problems occurring during plug-assisted vacuum thermoforming. This defect can occur during both the plug-assist and vacuum-forming stages. This article focuses on two issues: (1) the origins of fracture creation and (2) the determination of the process parameters needed for removal of the defect. The results of our work not only lead to an understanding of the cause of this problem but also enable us to calculate the parameters that affect the fracture of polymeric sheets during plug-assisted vacuum thermoforming. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 171-177, 2010